Polygon machining in which the outer peripheral surface of a workpiece is machined into a polygon or the like by using a polygon cutter is conventional. Polygon machining is carried out by rotating a workpiece gripped by a main shaft about the shaft line and by synchronously rotating the polygon cutter mounted to a tool spindle in a predetermined rotation ratio with respect to the workpiece.
There is a polygon machining method in which polygon machining is carried out after matching the phase of a workpiece with that of the polygon cutter between each piece of the polygon machining in the case where a plurality of kinds of polygon machining is carried out on the outer peripheral surface of a workpiece (e.g., see Patent Document 1).